In industrial plants employing screwed coupling members, a traction is generally applies to these members by means of a tensioning device, in order to keep them in a prestressed state and, during this traction, a nut for maintaining the coupling member in position is screwed or unscrewed.
This is particularly the case with pressure vessels employed, for example, in the nuclear, chemical or petrochemical industries, where a clamping and retaining nut must be screwed or unscrewed on each coupling member consisting, for example, of a stud, while traction is applied to all these coupling members by means of a tensioning nut also screwed onto each coupling member.
This is also the case in the motor and aircraft industries, where numerous screwed coupling members are employed.
These coupling members are generally employed in quite large numbers and relatively close to one another, with the result that on each occasion it is necessary to screw or unscrew the tensioning nut, on the one hand, and the retaining nut, on the other hand, on each coupling member.
These successive screwing and unscrewing operations on various nuts are long and tricky and can only be carried out automatically.